Field of the Invention
The embodiments disclosed herein relate generally to 3-D image generation and the identification and tracking of objects, and more particularly to LADAR sensors for mobile applications such as road hazard avoidance, collision avoidance, and autonomous navigation. The invention compensates for the issues arising from the operation of a multiplicity of ladar sensors operating simultaneously in a common environment allowing for a great number of LADAR sensors to be operated independently, and in close proximity.
References to Related Art
The 3-D imaging technology disclosed in Stettner et al, U.S. Pat. Nos. 5,446,529, 6,133,989 and 6,414,746 provides with a single pulse of light, typically pulsed laser light, all the information of a conventional 2-D picture along with the third dimensional coordinates; it furnishes the 3-D coordinates of everything in its field of view. This use is typically referred to as flash 3-D imaging in analogy with ordinary digital 2-D cameras using flash attachments for a self contained source of light. As with ordinary 2-D digital cameras, the light is focused by a lens on the focal plane of the LADAR sensor, which contains an array of pixels called a focal plane array (FPA). In the case of a LADAR sensor these pixels are “smart” and can collect data which enables a processor to calculate the round-trip time of flight of the laser pulse to reflective features on the object of interest.
Many systems have been proposed to meet the challenge of using optical imaging and video cameras in a vehicle system to create 3-D maps of scenes and models of solid objects, and to use the 3-D database to navigate, steer, and avoid collisions with stationary or moving objects. Stereo systems, holographic capture systems, and those which acquire shape from motion, have not been able to demonstrate adequate performance in this application, but 3D LADAR based systems have shown the ability to rapidly capture 3-D images of objects and roadway features in the path of a moving vehicle, or travelling on an intersecting path, with sufficient speed and accuracy to allow the host vehicle to avoid collisions and road hazards, and steer the best path. In an environment where many such vehicles are operating on the same roadway, it is foreseeable there will be many light pulses from many LADAR sensors mounted on the vehicles operating in the common operating space. It is therefore highly probable there will be light pulses impinging on LADAR receivers which did not originate from the associated laser transmitter. These spurious light pulses from other LADAR sensors could cause serious confusion, and false range measurements, unless means are developed to eliminate or reduce this probability. A layered approach to reducing this form of interference is detailed, including the use of a number of discrete laser wavelengths and receiver optical filters to prevent spurious transmissions from entering the LADAR receiver optical detectors, an assignment of discrete laser pulse widths and a pulse width discriminator, and a system of pulse encoding and pulse decoding to separate out spurious pulses. It is anticipated there will be a great number of LADAR sensors manufactured and installed on automobiles, and some laser transmitter wavelengths may have to be reused, and some laser pulse widths may also have to be reused. Therefore, it is a remote, yet finite possibility there will be spurious laser pulses which have passed through the receiver optical filter and pulse width discriminator.
It is therefore desirable to provide a LADAR system capable of operating in a “dense” environment to avoid computations based on improper laser pulses.